Did Dinosaurs Shrink and Evolve into Birds?

Chickens, crows, seagulls, and any other species of birds that one can think of, are largely believed to be modern-day dinosaurs. However, did the dinosaurs actually shrink and evolve into birds? Let's take a look at some facts related to this fascinating theory, and attempt to reach a feasible conclusion.

AnimalSake Staff

Did You Know?

Way back in 1859, British biologist Thomas Henry Huxley was the first person to propose that dinosaurs were feathered, and that they were the ancestors of modern birds.

The first dinosaurs were born around 240 million years ago. They were the largest creatures to roam the Earth, and they dominated the planet for several centuries. However, like all things, the age of the dinosaurs came to an end. Among many theories, it is generally believed that all of them died due to the cosmic impact of a comet/asteroid with the Earth. However, recent paleontology research has indicated that, this is not completely true. It is possible that some of the dinosaurs did not perish in the extinction event. Instead, they survived for millions of years more, all the while shrinking in size, and gradually evolving into birds.

Theory How Dinosaurs Shrank and Became Birds

It is thought that, birds evolved from the two-legged therapod class of dinosaurs, which included carnivores such as the tyrannosaurus rex, and raptors like the deinonchus. To learn how dinosaurs did evolve into birds, scientists created detailed family trees of known birds and dinosaurs, and mapped out anatomical traits of the creatures to see where the two lines separated from each other. They found that, therapods slowly shrunk and changed in shape over a long period of 50 million years, from a hefty 350 lbs to just 1.7 lbs. The evolution is also believed to have provided the dinosaurs with wings, smaller teeth, and larger brains and eyes. These changes gave them new abilities, such as gliding, flying, and climbing trees, which might have helped them survive the asteroid hit.

Evidence to Support the Theory

Initially, the archaeopteryx (a creature with feathered wings and body, but with teeth and a long, bony tail like a dinosaur) was the only link paleontologists had between dinosaurs and birds. However, as paleontologists studied over 1,500 anatomical features of more than 120 species of dinosaur fossils from different periods, they noticed many birdlike traits, such as three-fingered hands, hollow bones, feathers, wishbones, larger arms, beaks, forward posture, etc. Besides these, geneticists found that, with only a few tweaks in a bird's DNA, the facial structure could be made to look similar to that of a dinosaur.

Also, the skeleton sizes became consistently smaller, with the passage of time. Excavations in China, during the 1990s, uncovered numerous fossils of what appeared to be dinosaurs covered with fuzzy feathers or quills, which has strengthened their case even further. All these clues are indications of how dinosaurs became birds. These facts were accepted by a large part of the science community as proof of evolution. However, there is another group of researchers who disagree with this theory.

Criticisms of the Theory

Scientists conducting research found that, there were a few important points of differences between dinosaur and bird bodies, which made it unlikely that the evolution theory of dinosaurs turning to birds is true:

The accepted fact is that, all dinosaurs were reptiles, and by extension, cold blooded creatures, while birds are known to be warm-blooded. Change from cold-blooded body systems to warm-blooded systems is unprecedented, nor is there any proof to suggest that dinosaurs were actually warm-blooded, which is a major obstacle to the evolution process.

While supporters of the evolution theory display the three-fingered hand structure of dinosaurs to be similar to birds, the fact is that of the five fingers; dinosaurs retained digits 1, 2, and 3, while birds retained digits 2, 3, and 4.

The lungs of birds facilitate unidirectional airflow, unlike the bidirectional (air goes in and out using the same path) airflow of mammals. Although soft tissue is rarely found in dinosaur fossils, the ones which do, clearly show that their lungs were bidirectional in nature, rather than unidirectional like a bird.

A major blow to the evolution theory was the fact that, archaeopteryx fossils were much older than some dinosaur fossils, which is not possible if dinosaurs evolved into the archaeopteryx, before finally turning into birds.

It was also found that, all dinosaurs would run or walk using their hips, but birds move using the knee joints, while the hips remain largely stationary. While this does not seem very significant a change, the fact is that, the immobility of a bird's hip keeps its lungs from collapsing, which seems to contradict the dinosaur-to-bird theory.

While the above arguments do not provide indisputable proof for either theory, it is interesting to see how the field of paleontology is shaping up towards the future. Researchers use huge data sets, which compile information on facts such as family trees and physical characteristics. Paleontologists have to now be as comfortable with complex math, biology, and computer programs, as they are with their rock picks and hammers. As for whether birds truly evolved from dinosaurs, we will require many more fossils of complete dinosaur skeletons to reach a definitive answer.